Substantially helical, stepped blade row cutterhead having removable blade units

ABSTRACT

A cutterhead for a peripheral milling machine including a cutterhead body including a generally cylindrical portion and a plurality of circumferential, spaced and offset blade unit mounting cavities extending into the cutterhead body from the periphery of the cylindrical portion for receiving a blade unit. The cutterhead further includes a plurality of blade units each having at least one cutting edge and means for removably securing each of the removable blade units in the corresponding blade unit mounting cavity. The cutting edge of each of the blade units is disposed to align with the cutting edge of each of the other blade units in adjacent mounting cavities to form a substantially helical, stepped blade row when the blade units are secured to the cutterhead body.

BACKGROUND

(1) Field of the Invention

The present invention relates generally to cutterheads for peripheralmilling machines, which includes surfacers, planers, molders, joinersand similar machines, and, more particularly, to a substantiallyhelical, stepped blade row cutterhead having removable blade units.

(2) Description of the Prior Art

The present invention relates to improvements in cutterheads,particularly cutterheads such as those shown in the applicant's commonlyowned U.S. Pat. Nos. 4,074,737, 5,002,104, 5,653,275, 5,603,365,5,647,416, and 5,738,156, the entire disclosures of which areincorporated herein by reference in their entirety.

Helical cutterheads for peripheral milling machine that have particularpitch arrangements reduce the noise generated by the cutterhead whileplaning a workpiece. These cutterheads generally have a plurality ofsegmented cutterhead inserts, each of which includes a cutting blademounted in cooperating or receiving grooves in the cutterhead body. In atypical arrangement, the cutterhead inserts span about one inch alongthe cutterhead length. The cutterhead inserts are securely mounted inthe grooves to form substantially continuous blade rows. The contour ofthe actual cutting edge of the blade rows preferably follows the contourof the helical groove in the cutterhead.

In one embodiment described in the above patents, the cutterhead insertshave carbide cutting blades brazed or welded to them. The carbide blade,after brazing to the cutterhead insert, is subsequently ground to obtaina helical geometry in keeping with the entire helix of the cutterhead.When the cutting blade is worn out, the entire cutterhead insert must bereplaced or returned to a tool shop for re-tipping and regrinding.

In the prior art cutterheads, the brazing method of attachment limitsthe materials that can be used as the cutting blades to those that canwithstand brazing, such as conventional carbide. However, more advancedcutting materials including diamonds, ceramics, coated materials, highcobalt alloys, etc. would be difficult to braze and impractical to useas the entire cutterhead insert. The other patents teach various ways toprovide removable blade units to in order to eliminate the need forbrazing and simplify the re-tipping process, which requires a highdegree of skilled labor.

Thus, there still remains a need for an improved cutterhead that permitsother blade materials to be used to form the cutting edge while, at thesame time, reduces maintenance by eliminating regrinding and providingfor simple blade unit replacement as they are worn or damaged.

SUMMARY OF THE INVENTION

This disclosure describes a cutterhead for a peripheral milling machine.The cutterhead includes a cutterhead body including (a) a generallycylindrical portion and (b) a plurality of circumferential, spaced andoffset blade unit mounting cavities extending into the cutterhead bodyfrom the periphery of the cylindrical portion for receiving a bladeunit. The cutterhead further includes a plurality of blade units eachhaving at least one cutting edge and means for removably securing eachof the removable blade units in the corresponding blade unit mountingcavity. The cutting edge of each of the blade units is disposed to alignwith the cutting edge of each of the other blade units in adjacentmounting cavities to form a substantially helical, stepped blade rowwhen the blade units are secured to the cutterhead body. In anembodiment, the blade unit mounting cavities are offset and overlapped.The minimum offset to provide an overlapping corner of an adjacent bladeunit cutting edge is a function of the shear angle orientation of theblades and the geometry of the blade units whereby each helical steppedblade row makes a full cut.

The minimum offset of the blade units may be calculated according to thefunction Minimum Offset equals (w′)(tangent(90°−shear angle°)); where w′is the blade unit width dimension and the shear angle is the angleformed by the blade unit and the rotational axis of the cutterhead. Thecutterhead body may further include a chip deflector, which may beintegrated into the blade unit, or, alternatively, be a separate platelocated in the blade mounting cavity beneath the blade and thecutterhead may be made of steel, aluminum or similar materials.

The blade unit mounting cavities may extend into the cutterhead bodyfrom the periphery of the cylindrical portion for receiving a blade unitand further include a corner relief. Also, the cavities may include atilt angle, calculated to minimize the error in fit to the desiredhelical cure, and by a roll angle, which determines the offset of thefront face of a given blade unit with respect to the front face of anadjacent blade unit.

The apparatus may further include means for removably securing each ofthe removable blade units in the corresponding blade unit mountingcavity and each of the blade unit mounting cavities may include a holeto receive the means for removably securing a blade unit in itsrespective mounting cavity. The means for removably securing the bladeunit in its respective mounting cavity may be a fastener, which may be athreaded fastener, and the hole in the blade unit may be countersunk.

Furthermore, each of the mounting cavities may include at least oneraised portion and each of the blade units have at least three sides andat least one side that abuts the raised portion of a blade unit mountingcavity and the blade units may have four cutting edges. In addition, theholes for the threaded fasteners may be offset to provide mating of theblade units with the raised portion of the mounting cavities and toprovide that cutting forces act on the raised portion of the mountingcavities and not on the fasteners, thereby helping to prevent failure ofthe fasteners and movement of the blade unit.

The blade units may be inverted truncated pyramids having a thickness ofpreferably less than about 10 mm and the cutting faces of the bladeunits may be radiused to conform more closely to the approximatedhelical curve. Also, the cutting edge of each of the blade units may beraised to facilitate jointing, and each of the mounting cavities mayinclude a dimple or recess with each of the blade units including amating dimple or recess.

The blade units may be made of materials selected from the groupconsisting of diamond, ceramic, carbide, high cobalt alloys, and highspeed steel and mixtures thereof, and they may be coated, implanted ordeposited to reduce wear using techniques including growth of CVD andPVD diamond films, titanium nitride and similar coatings, and may alsobe hardened using heat treatments or cryogenic treatments.

Accordingly, one aspect of the present invention is to provide acutterhead for a peripheral milling machine. The cutterhead includes acutterhead body including (a) a generally cylindrical portion and (b) aplurality of circumferential, spaced and offset blade unit mountingcavities extending into the cutterhead body from the periphery of thecylindrical portion for receiving a blade unit. The cutterhead furtherincludes a plurality of blade units each having at least one cuttingedge. Each cutting edge of each of the blade units is disposed to alignwith the cutting edge of each of the other blade units in adjacentmounting cavities to form a substantially helical, stepped blade rowwhen the blade units are secured to the cutterhead body.

Another aspect of the present invention is to provide a cutterhead bodyfor a cutterhead for a peripheral milling machine having a plurality ofblade units each having at least one cutting edge. The cutterhead bodyincludes a generally cylindrical portion and a plurality ofcircumferential, spaced and offset and overlapped blade unit mountingcavities extending into the cutterhead body from the periphery of thecylindrical portion for receiving a blade unit. The cutting edge of eachof the blade units is disposed to align with the cutting edge of each ofthe other blade units in adjacent mounting cavities to form asubstantially helical stepped blade row when the blade units are securedto the cutterhead body and the minimum offset to provide an overlappingcorner of an adjacent blade unit cutting edge is a function of the shearangle orientation of the blades and the geometry of the blade unitswhereby each helical stepped blade row makes a full cut.

Still another aspect of the present invention is to provide a cutterheadfor a peripheral milling machine. The cutterhead includes a cutterheadbody including (a) a generally cylindrical portion and (b) a pluralityof circumferential, spaced and offset and overlapped blade unit mountingcavities extending into the cutterhead body from the periphery of thecylindrical portion for receiving a blade unit. The cutterhead furtherincludes a plurality of blade units each having at least one cuttingedge and means for removably securing each of the removable blade unitsin the corresponding blade unit mounting cavity. The cutting edge ofeach of the blade units is disposed to align with the cutting edge ofeach of the other blade units in adjacent mounting cavities to form asubstantially helical stepped blade row when the blade units are securedto the cutterhead body and the minimum offset to provide an overlappingcorner of an adjacent blade unit cutting edge is a function of the shearangle of the helical stepped blade row edge and the geometry of theblade units whereby each helical stepped blade row makes a full cut.

These and other aspects of the present invention will become apparent tothose skilled in the art after a reading of the following description ofthe preferred embodiment when considered with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of a cutterhead for a peripheralmilling machine constructed according to the present invention;

FIG. 2 a is an enlarged front perspective view of a portion of thecutterhead of FIG. 1 with the blade units removed;

FIG. 2 b is an enlarged front perspective view of a portion of thecutterhead of FIG. 1 with the blade units attached;

FIG. 3 is enlarged view of the end portion of the cutterhead;

FIG. 4 is a top perspective view of an embodiment of a fastener andblade combination;

FIG. 5 is a top perspective view of another embodiment of a fastener andblade unit combination;

FIG. 6 is a side cross-sectional view of another embodiment of a bladeunit;

FIG. 7 is a side cross-sectional view of another embodiment of a bladeunit;

FIG. 8 is an enlarged side view of the end portion of the cutterhead;

FIG. 9 is an enlarged top view of the end portion of the cutterhead;

FIG. 10 is an enlarged end view of the end portion of the cutterhead;

FIGS. 11 e(a), (b) and (c) are schematics illustrating the relativepositioning of blade units at various shear angles for achieving anoverlap cut;

FIG. 12 is a graphical representation of the Minimum Blade Unit Offsetper Blade Unit Spacing versus the Shear Angle of a Blade Unit;

FIGS. 13( a), (b) and (c) illustrate the surface marks of work piecesdepending on the arrangement of the blade units;

FIG. 14 shows a blade unit having curved faces;

FIG. 15 shows an alternative embodiment of a cutterhead having a singleblade row;

FIG. 16 is a graphical representation of the Maximum Shear Angle versusthe Width of a Blade Unit; and

FIG. 17 is a graphical representation of the Minimum Required Overlapper Unit Wear Land.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, like reference characters designate likeor corresponding parts throughout the several views. Also in thefollowing description, it is to be understood that such terms as“forward,” “rearward,” “left,” “right,” “upwardly,” “downwardly,” andthe like are words of convenience and are not to be construed aslimiting terms.

Referring now to the drawings in general and FIG. 1 in particular, theillustrations are for the purpose of describing embodiments of acutterhead and are not intended to limit the invention thereto. FIG. 1shows a cutterhead 10 for a peripheral milling machine. The cutterhead10 includes a cutterhead body 20 that can be constructed from steel,aluminum or similar materials and include one or more body units 22,each of which includes a generally cylindrical portion 24 and aplurality of blade units 30. Each of the blade units 30 includes acutting edge 32 disposed with respect to a cutting edge 32 of adjacentblade units 30 to form a substantially helical, stepped blade row 40with blade units 30 in well defined rows with minimum offset betweenblade units 30 to produce planer marks similar to those produced byconventional cutterheads and permit large numbers of rows for high-speedapplications of the cutterhead 10. With the body units 22 alignedaxially on an arbor 14, the substantially helical, stepped blade row 40can extend from body unit 22 to adjacent body unit 22, as shown inFIG. 1. Blade unit 30 positioning is calculated to provide a “best-fit”helical curve.

FIGS. 2A and 2B show a body unit 22 that includes a plurality ofcircumferential, spaced and offset blade unit mounting cavities 50extending into the unit 22, and thus, the cutterhead body 20, from theperiphery 25 of the generally cylindrical portion 24 of the unit 22.Each of the blade unit mounting cavities 50 includes a hole 52 forreceiving a fastener for securing a blade unit 30 in the mounting cavity50 to provide an overlapping corner 8. The body unit 22 shown can beused alone or in combination with other, similar body units to form thecutterhead 10 having four blade rows 40, although only one is requiredto make a complete cut.

FIG. 3 shows a mounting cavity 50 including a flat seat area 52 andraised portions 53 and 54 along a back and side of the cavity 50,respectively. The mounting cavity 50 shown also includes optionaldepressions 56 that provide blade unit corner relief. In addition, thehole 60 may be offset to provide mating of the blade unit 30 with theraised portions 53 and 54 of the mounting cavities. Also, the cavity 50may have a recess or dimple for mating with a dimple or recess in ablade unit.

FIG. 4 shows an embodiment of the blade unit 30(a) in the shape of aninverted truncated pyramid and a mating fastener 42(a) for securing theblade unit 30 in one of the mounting cavities shown in FIG. 2. Thefastener 42(a) includes a threaded rod 44(a) below a flange 45(a) shapedto seat within a mating cavity 31(a) in the blade unit 30(a) tocountersink the fastener flange 42(a). Any one of four cutting edges 36can be rotated to form a portion of the substantially helical, steppedblade row 40 shown in FIG. 1.

FIG. 5 shows an alternative embodiment of the blade unit 30(b) andfastener 42(b) shown in FIG. 4. This unit 30(b) and fastener 42(b)combination is designed for especially high impact applications of thecutterhead 10, and thus includes two opposing cutting edges 36 and twodubbed off edges 47. Alternative screw design 42(b) removes lesscross-sectional area for the countersink 31(b) in blade unit 30(b),which thereby strengthens the blade unit 30(b) and improves its breakageresistance. The flange 45(b) mates with the mounting cavity 31(b) toincrease the strength of the fastener 42(b) and blade unit 30(b)combination. This fastener 42(b) and unit 30(b) combination alsoincreases the strength of the corners of the unit 30(b) versus that ofFIG. 4 by eliminating the compound angles required in the corners of theembodiment of the unit 30(a) shown in FIG. 4.

Alternative embodiments for increasing the impact resistance of theblade units include combinations of the screw design, rounding of thecorners and dubbing or flattening of opposite sides of the blade units30 to form two sided blade units. The blade units 30 may includematerials such as diamond, ceramic, carbide, high cobalt alloys, highspeed steel and mixtures thereof, and the thickness 49 of the bladeunits 30(a) and 30(b) may preferably be less than about 5 mm.

FIGS. 6 and 7 show the typical work piece chip flow from the cuttingedges 32(c) and 32(d) of blade units 30(c) and 30(d), respectively, intochip gullet areas 57 associated with each of the mounting cavities 50shown in FIG. 2. In the embodiments shown in FIGS. 6 and 7, each of theblade units 30(c) and 30(d) includes a chip deflection device 39(a) and39(b) to prevent wear in the chip gullet areas 57 that would otherwisebe caused by the chip flow, especially in high-speed applications of thecutterhead. The device 39(a) is molded into the blade unit 30(c) whereasthe blade unit 30(d) includes a separable deflection plate 39(b) in theseat area 52 of the blade unit cavity 50.

FIG. 8 shows the tilt angle 80 of the blade units 30 with respect to anaxis 82 perpendicular to the axis 81 of rotation of the cutterhead body20. The tilt angle is calculated to compensate for geometry errors dueto the shear angle. Preferably, the tilt angle 80 is between about 2 and5 degrees. For applications where a relatively small diameter cutterheadbody 20 is desirable, the tilt angle 80 may be larger.

FIG. 9 shows the shear angle 110 of a blade unit 30, which is the anglethat is formed between the axis of rotation 81 of the cutterhead 10 anda cutting edge 36. Although it is possible to use the cutterhead with ablade unit 30 shear angle of 0°, increasing the shear angle 110 resultsin more continuous cutting forces, which reduce noise, vibration, bladeunit edge wear and improves surface quality.

FIG. 10 shows the roll angle 90 of the blade units 30, which is theangle formed by the offset of one cutting edge 36 with respect to theadjacent cutting edge 36. The offset provides improved workpiece chipbreaking by producing shorter chips than a conventional helicalcutterhead, which increases the efficiency of the chip collection systemof the peripheral milling machines since longer chips tend to clog thechip collection tubes. The figure also shows the tip projection 96 andclearance angle 97 for a unit 30. The tip projection 96 is the radialdistance that the cutting edge 36 of a unit 30 extends beyond thegenerally cylindrical portion of the cutterhead body 20. A larger tipprojection 96 permits higher feed rates, increased depths of cut, andfacilitates honing (jointing) of the cutting edges 36 to increasecutting efficiency after the edges become worn. The clearance angle 97is the angle between a line parallel to the top surface of the bladeunit 30 and a line perpendicular to the vertical axis 95 when the bladeunit cutting edge 36 is positioned on the vertical axis 95. Generally,an increase in the clearance angle may reduce surface defects and alsoaids in jointing of the blade cutting edges 36 when needed.

FIGS. 11( a), 11(b) and 11(c) show schematically the relativepositioning of blade units 30 required to achieve an overlap cut, whichresults when one area of the work piece is machined by each of twoadjacent blade units 30. This overlap provides that a completed cut istaken by a single knife row. Because the geometry of the corners of theunits may make them susceptible to breakage, an overlap cut provides agreater likelihood that corresponding areas of the work piece will bemachined when adjacent blade units 30 have broken corner areas. As theshear angle 110 decreases, the offset 112 between adjacent units 30 mustbe increased or the distance 114 between blade units 30 decreased tomaintain an overlap cut. Since the distance 114 is preferably held to aminimum in the present inventions, this generally results in an increasein the offset. However, the figure shows the relative positioning of theblade units 30 in two dimensions. When the blade units 30 are mounted inthe cavities of a cutterhead body, of course, the radius of thegenerally cylindrical portion introduces a third dimension to therelationship that is not depicted by the figure, but the relationshipbetween the blade units 30 in the two dimensions shown remains.

FIG. 11 also illustrate how the present inventions improve blade unitcutting edge life. The shear angle provides improvements in edge lifeover conventional straight blade units by reducing the fluctuating(impulsive) forces acting on the cutting edge. This reduces themicro-chipping wear of the edge associated with the normal machiningprocess and results in significant increases in edge life. Indexibleblade units typically have weakened corners resulting from multiplecutting edges, which often break or chip before the blade unit wouldotherwise be taken out of service. This results in reduced blade unitlife due to only two opposite sides (for a blade with four edges) areuseable. The overlap utilized in the current inventions, as illustratedin FIG. 11, provides protection for the trailing corner and results in adouble cut in the overlap zone. These features, acting together, usuallyresults in defect free cutting if either one of the corners is chippedor damaged, which usually allows all four edges to be used for theirnormal life. For high impact high breakage applications, this may resultin as much as a doubling of total blade unit life.

FIG. 12 is a graph showing the relationship between the Shear Angle ofthe Blade Units and the Minimum Blade Unit Offset per Unit Spacingbetween the blade units. As can be seen, the minimum offset to providean overlapping corner 8 of the blade units follows the function MinimumOffset equals (w′)(tangent(90°−shear angle°)); where w′ is the bladeunit width dimension and the shear angle is the angle formed by theblade unit and the rotational axis of the cutterhead.

FIGS. 13( a), (b) and (c) are illustrations of surface marks expected tobe produced in workpieces by peripheral milling machine operations usingvarious cutterheads. FIG. 13( a) shows the surface marks produced by atrue continuous helical cutterhead blade, which are similar toconventional straight knife head cutter marks. FIG. 13( b) shows theirregular surface marks produced by a conventional stagger toothcutterhead. FIG. 13( c) shows the surface marks of the substantiallyhelical, stepped blade row cutterhead having removable blade units ofthe present inventions. As can be seen, these surface marks more closelyresemble those of a true continuous helical cutterhead shown in FIG. 13(a), than do the marks left by a conventional stagger tooth cutterhead inFIG. 13( b). This type of surface finish is more commercially desirablefor many applications.

FIG. 14 shows a blade unit 30 including four cutting faces 32 having aradius of curvature of about 150 mm.

FIG. 15 shows an alternative embodiment of a cutterhead 10 having asingle blade row 40.

FIG. 16 is a graphical representation of the Maximum Shear Angle versusthe Width of a Blade Unit for several cutterhead diameters (D).

FIG. 17 is a graphical representation of the Minimum Overlap Requiredper Unit Wear Land to insure a complete cut.

Certain modifications and improvements will occur to those skilled inthe art upon a reading of the foregoing description. By way of example,other known types of chip management and tear out control could beutilized. Also, different orientations of the shear cutting faces withrespect to the axis of rotation may be used to improve chip collectionand improve workpiece edge quality. These variations include right handshear geometry, left hand shear geometry, and compression sheargeometry. The importance of these configurations is due to the oppositedirections of chip flow for right and left hand shear cutting (whichaffects chip collection efficiency) and the effect of shear angleorientation on workpiece edge tearout (chipping, splintering, etc.).

For surfacing applications using either a right hand or left hand shearorientation, the forces acting on the edges of a workpiece are “into”the workpiece edge on one side of the workpiece (which reduces chipping)and “off” the edge for the other side of the workpiece (which increaseschipping). These problems are exaggerated for higher shear angles. Thecompression design, which is used for applications involving a specificrange of workpiece widths, may incorporate a left hand shear on one endof the cutter and a right hand shear on the other end of the cutter soas to achieve “into” the edge cutting on both sides of the workpiece,thereby reducing workpiece damage.

Furthermore, the blade units may also be coated, implanted or depositedon the rake or clearance face with additional wear resistant materialsso as to promote a differential wear rate between the rake and clearancefaces, which results in a “self sharpening” effect. The use of coatingsand other wear resistant technologies can also be used to reduceincidental wear occurring on blade unit edges, which are not associatedwith the cutting action due to the flow of chips.

Finally, the cutterhead may contain a large number of blade rows toaccommodate high speed applications. This may also incorporate profilingblade units that are located in mounting cavities machined into thesides of the cutterhead body and may be adjusted for profile width bythe addition or removal of shims between the blade unit and the seat ofthe mounting cavity. All such modifications and improvements have notbeen included herein for the sake of conciseness and readability but areproperly within the scope of the following claims.

1. A cutterhead for a peripheral milling machine, said cutterheadcomprising: (a) a cutterhead body including (i) a generally cylindricalportion and (ii) a plurality of circumferential, spaced and offset bladeunit mounting cavities extending into the cutterhead body from theperiphery of the cylindrical portion for receiving a blade unit; and (b)a plurality of blade units each having at least one cutting edge,whereby said cutting edge of each of said blade units is disposed toalign with the cutting edge of each of the other blade units in adjacentmounting cavities to form a substantially helical, stepped blade rowwhen said blade units are secured to said cutterhead body, whereby theminimum offset to provide an overlapping corner of an adjacent bladeunit cutting edge is a function of the shear angle orientation of theblades and the geometry of the blade units, wherein the minimum offsetis calculated according to the function Minimum Offset equals(w′)(tangent(90°−shear angle°)); where w′ is the blade unit widthdimension and the shear angle is the angle formed by the blade unit andthe rotational axis of the cutterhead, whereby each helical steppedblade row makes a full cut.
 2. The apparatus according to claim 1,further including a fastener for removably securing each of saidremovable blade units in said corresponding blade unit mounting cavity.3. The apparatus according to claim 2, wherein each of said blade unitmounting cavities include a hole to receive the fastener for removablysecuring the blade unit in its respective mounting cavity.
 4. Theapparatus according to claim 3, wherein said hole is countersunk.
 5. Theapparatus according to claim 4, wherein said fastener is a threadedfastener.
 6. The apparatus according to claim 1, wherein each of saidmounting cavities includes at least one raised portion and each of saidblade units have at least three sides and at least one side that abutsthe raised portion of a blade unit mounting cavity.
 7. The apparatusaccording to claim 6, wherein said blade units have four cutting edges.8. The apparatus according to claim 7, wherein said blade units areinverted truncated pyramids.
 9. The apparatus according to claim 6,wherein the thickness of said blade units is less than about 10 mm. 10.The apparatus according to claim 6, wherein the radius of curvature ofsaid blade units is between about 0 and 250 mm.
 11. The apparatusaccording to claim 6, wherein the cutting edge of each of said bladeunits is raised to facilitate jointing.
 12. The apparatus according toclaim 1, wherein said blade units are made of materials selected fromthe group consisting of diamond, ceramic, carbide, high cobalt alloys,and high speed steel and mixtures thereof.
 13. The apparatus accordingto claim 12, wherein said blade units are coated, implanted or depositedto reduce wear using techniques including growth of CVD and PVD diamondfilms, titanium nitride and similar coatings, and may also be hardenedusing heat treatments or cryogenic treatments.
 14. A cutterhead body fora cutterhead for a peripheral milling machine having a plurality ofblade units each having at least one cutting edge, said cutterhead bodycomprising: (a) a generally cylindrical portion; and (b) a plurality ofcircumferential, spaced and offset and overlapped blade unit mountingcavities extending into the cutterhead body from the periphery of thecylindrical portion for receiving a blade unit, whereby said cuttingedge of each of said blade units is disposed to align with the cuttingedge of each of the other blade units in adjacent mounting cavities toform a substantially helical stepped blade row when said blade units aresecured to said cutterhead body and whereby the minimum offset toprovide an overlapping corner of an adjacent blade unit cutting edge isa function of the shear angle orientation of the blades and the geometryof the blade units, wherein the minimum offset is calculated accordingto the function Minimum Offset equals (w′)(tangent(90°−shear angle°));where w′ is the blade unit width dimension and the shear angle is theangle formed by the blade unit and the rotational axis of thecutterhead, whereby each helical stepped blade row makes a full cut. 15.The apparatus according to claim 14, wherein the cutterhead body furtherincludes a chip deflector adjacent to each of said mounting cavities.16. The apparatus according to claim 14, wherein said cutterhead is madeof steel, aluminum or similar materials.
 17. The apparatus according toclaim 14, wherein said blade unit mounting cavities extending into thecutterhead body from the periphery of the cylindrical portion forreceiving a blade unit further includes a corner relief.
 18. Theapparatus according to claim 14, wherein said blade unit mountingcavities extending into the cutterhead body from the periphery of thecylindrical portion for receiving a blade unit further includes a tiltangle for improving the helical curve fit for a predetermined shearangle.
 19. The apparatus according to claim 14, wherein said blade unitmounting cavities extending into the cutterhead body from the peripheryof the cylindrical portion for receiving a blade unit further includes aroll angle for adjusting the offset for overlapping blade units.
 20. Acutterhead for a peripheral milling machine, said cutterhead comprising:(a) a cutterhead body including (i) a generally cylindrical portion and(ii) a plurality of circumferential, spaced and offset and overlappedblade unit mounting cavities extending into the cutterhead body from theperiphery of the cylindrical portion for receiving a blade unit; (b) aplurality of blade units each having at least one cutting edge; and (c)a fastener for removably securing each of said removable blade units insaid corresponding blade unit mounting cavity, whereby said cutting edgeof each of said blade units is disposed to align with the cutting edgeof each of the other blade units in adjacent mounting cavities to form asubstantially helical stepped blade row when said blade units aresecured to said cutterhead body and whereby the minimum offset toprovide an overlapping corner of an adjacent blade unit cutting edge isa function of the shear angle orientation of the blades and the geometryof the blade units, wherein the minimum offset is calculated accordingto the function Minimum Offset equals (w′)(tangent(90°−shear angle°));where w′ is the blade unit width dimension and the shear angle is theangle formed by the blade unit and the rotational axis of thecutterhead, whereby each helical stepped blade row makes a full cut. 21.The apparatus according to claim 20, wherein each of said blade unitmounting cavities include a hole to receive the fastener for removablysecuring the blade unit in its respective mounting cavity.
 22. Theapparatus according to claim 21, wherein said hole is countersunk. 23.The apparatus according to claim 22, wherein said fastener is a threadedfastener.
 24. The apparatus according to claim 20, wherein each of saidmounting cavities includes at least one raised portion and each of saidblade units have at least three sides and at least one side that abutsthe raised portion of a blade unit mounting cavity.
 25. The apparatusaccording to claim 24, wherein said blade units have four cutting edges.26. The apparatus according to claim 25, wherein said blade units areinverted truncated pyramids.
 27. The apparatus according to claim 24,wherein the thickness of said blade units is less than about 10 mm. 28.The apparatus according to claim 24, wherein the radius of curvature ofsaid blade units is between about 0 and 250 mm.
 29. The apparatusaccording to claim 24, wherein the cutting edge of each of said bladeunits is raised to facilitate jointing.
 30. The apparatus according toclaim 20, wherein said blade units are made of materials selected fromthe group consisting of diamond, ceramic, carbide, high cobalt alloys,and high speed steel and mixtures thereof.
 31. The apparatus accordingto claim 30, wherein said blade units are coated, implanted or depositedto reduce wear using techniques including growth of CVD and PVD diamondfilms, titanium nitride and similar coatings, and may also be hardenedusing heat treatments or cryogenic treatments.
 32. The apparatusaccording to claim 20, wherein the cutterhead body further includes achip deflector adjacent to each of said mounting cavities.
 33. Theapparatus according to claim 20, wherein said cutterhead is made ofsteel, aluminum or similar materials.
 34. The apparatus according toclaim 20, wherein said blade unit mounting cavities extending into thecutterhead body from the periphery of the cylindrical portion forreceiving a blade unit further includes a corner relief.
 35. Theapparatus according to claim 20, wherein said blade unit mountingcavities extending into the cutterhead body from the periphery of thecylindrical portion for receiving a blade unit further includes a tiltangle for improving the helical curve fit for a predetermined shearangle.
 36. The apparatus according to claim 20, wherein said blade unitmounting cavities extending into the cutterhead body from the peripheryof the cylindrical portion for receiving a blade unit further includes aroll angle for adjusting the offset for overlapping blade units.